Seal for electric devices



Patented May 22, 1923.

,UNITED STATES PATENT- OFFICE.

. GEORGE MACKAY, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC-TRIO COMPANY, A CORPORATION OF NEW YORK.

SEAL roa ELECTRIC DEVICES.

Application filed J'an'uary 21, 1921. Serial No. 438,899.

To all whom it may con/cm:

Be it known that I, Gnonen M. J. Mao- KAY, a citizen of the UnitedStates, residing for Electric Devices, of which the following is aspecification.

and shell. My

The present invention comprises a new seal for electric devices which isparticularly useful for making a gas-tight seal in containers consistingof electrically conductive material.

' It is often highly desirable and sometimes necessary to encloseelectrical apparatus within a sealed metal container. For example,refrigerating apparatus utilizing irritating or poisonous gases areenclosed advantageously in a sealed metal receptacle. In other cases,highl evacuated devices, such, for example, as ra tubes and electrondischarge devices of a l sorts, also electric are devices in some casesare provided with metal enclosures, particularly when of high currentcapacity. In all such cases, it is necessary to pass an insulatedelectrical conductor into the metal enclosure, and it has always been aserious problem to provide electrical insulation which will withstandvariations of temperature and mechanical shocks without permitting theleakage of gas in orout of the sealed container.

As a result of my invention -I have provided an electrical conductor.capable of bein sealed into a metal container and comrislng a conductivecore surrounded by a layer of vitreous material which is in turnsurrounded by and maintained under compression by a metallic shell, the-vitreous nvention includes both a new article and thb method of makingthe article.

In the accompanying drawing, Fig. 1 is a longitudinal section of aninsulated conductor embodyin myiinvention; and Fig. 2 is a end view 0 amultiple conductor embodying an invention.

. Fig. 1 s ows the finished article consisting of a shell or sleeve 1,an axially located ,core 2 and an intervening layer of vitreous material3. The shell has been screwthreaded at 4 for convenience of attachment.

In the preparation of a composite conductor embodying my invention, theconductor core 2 is threaded thru a tube 3 of glass 1 and these twoelements of the conductor are in turn surrounded by a metallic shell orsleeve 1. The original members when assembled may have the diameter'ofthe screwthreaded part 4, as shown in the drawing, the reduced diameterof the adjoining section being produced by the subsequent swaging. Thesurface of the core, and the inner face of the shell are adapted, aslater described, to be wetted by the vitreous material when lastic so asto produce a gastight seal. For example, when using ordinary lead glassas the insulating and sealing layer 3, I employ preferably a core 2consisting of a nickel iron alloy having a somewhat lower expansioncoefficient than lead glass, and provided with a superficial layer ofcopper. The wine as a whole has approximately the same coeiiicient ofexpansionas lead glass. Copper coated tungsten or molybdenum may besimilarly used. The shell may consist of steel coated with copper uponthe inner surface which is in contact with the glass layer, or it mayconsist of copper, and various other materials. In the case be chosensomewhat higher than the expansion coefiicient of the glass. IngeneraLthe expansion coeflicient of the core should be equal to orsomewhat lower than that of the vitreous layer, while the expansioncoefficient of the shell preferably should be somewhat higher than thatof the vitreous layer. It is possible, althou h not preferable, to

produce my new artic e when the expansion coefficient of the core, shelland intervening glass layer are all equal.

Before assembly the surface of the core and the inner surface of theshell are treated with a borax solution in accordance with the processdescribed in Van Keuren Patent 1,268,647 of June 4,1918. Thereupon, thecore, insulator and shell are assembled and heated to a temperature atwhich the insulator is plastic. but not fluid. In the case of lead glassabout 800 C. is a suitabletemperature for working. The insulatedconductor when assembled and heated to a workable condition is swaged orotherwise treated to reduce its diameter. A suitable swaging mechanismis described in U. S. Patent 1,082,933 of December 30, 1913. As by thistreatment the diameter of the shell and insulator is reduced, theinitial diameterof the article prior to swaging should be reater thanthe desired diameter of the completed articles. The reduction indiameter due to swaging is shown in the drawing by contrast with thescrew-threaded part 4. The diameter of the core remains substantiallyunchanged by the swaging treatment. A firm adherence of the insulator 3with the core and. the shell are produced while the glassy mass remainsunbroken. This treatment may be repeated with intervenin reheating untilthe article has been recuced to a desired diameter. The mass of vitreousmaterial is maintained under pressure by the shell when the thermalexpansion coefiicient of theshell is somewhat greater than the expansioncoefiicient of the glass.

In the same way an article containing a plurality of insulatedconductors may be produced, as illustrated in Fig. 2. The article hereillustrated may be made by proceeding in essentially the same manner asabove described. A cylinder 5 (shown at end) consisting, for example, ofordinary carbon steel is bored out at a desired number of places toproduce openings running lengthwise through the cylinder. The walls ofthese openings preferably are plated with cop er and borated. A thickwalled tube 6 0 glass, or the like containing a conductor 7 closed andprepared as above described are inserted and the whole article thusassembled is heated and swaged while the glass is plastic to cause theglass layers 6 to be firmly packed in the massive state in the spaceintervening between the core and shell. The cylinder 5 finally may bemachined in any desired manner and inserted in a metal enclosure, orused in any other desired manner. Preferably the completed articles arecooled slowly to anneal the same.

As result of my invention an insulated seal for an electrical conductoris produced which remains gas impervious even when subjected to changesof temperature and mechanical vibration, or shocks.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is 1. A as-tightseal comprisin -a core of conductive material, alayer 0 glass surrounding said core, and a metallic shell surroundingsaid glass layer, the glass layer making a gas-tight'joint with saidcore and shell.

2. An article of manufacture comprising the combination of a conductor,a surrounding shell and an intermediate layer of vitreous materialadhering to said core and shell, and being homogeneous andgas-impervious.

3. An article of manufacture comprising an enclosing shell, a core ofconductive material therein spaced away from said shell and a layer ofvitreous material adhering to said core and shell and filling theintervening space in a gas-impervious condition, the thermal coefiicientof expansion of said shell being at least as great as that of saidvitreous material, and the thermal coetlicient of said core being nogreater than the expansion coefiicient of said material.

4. A seal for electric devices comprising in combination a cylindricalshell of metal,

,a core of conductive material spaced away from said shell and a unitarymass of vitreous material completely filling the space be tween saidcore and shell in a gas-impervious state.

5. The method of making a gas-impervious insulating seal between aconductor and an enclosing metal shell which consists in interposingbetween said conductor and said shell a mass of vitreous material,heating said assembled article to the softening telnperature of saidvitreous material, and me chanically reducing the diameter of said shellwhile thus heated, thereby causing said vitreous material to completelyfill the space between said core and shell, and to adhere to thecontiguous surfaces of said core and shell.

6. A seal for electric devices comprising the combination of a core ofnickel-iron alloy having a lower coeflicient of expansion than leadglass and provided with a coating of copper, a layer of lead glasssurrounding said core and a shell of steel having the inner surfacethereof coated with a flux, compressively surrounding said glass layer,the contiguous surfaces of members adhering to each other in a gas-tightcondition.

In witness whereof, I have hereunto set my hand this 17th day ofJanuary, 1921.

GEORGE M. J. MACKAY.

